Insulated wire or cable

ABSTRACT

Insulated wire or cable having primary insulation between copper conductor and moisture barrier filler and wherein the primary insulation comprises: 
     Ethylene polymer having a density of about 0.928 to 0.955, 
     Copper deactivating amounts of at least one organic compound which is an oxalyl dihydrazide, and 
     Antioxidant effective quantities of at least one organic compound having a molecular weight of ≧550 and which contains 2 or 3 hindered phenolic groups per molecule thereof.

This is a division of application Ser. No. 312,033 filed Dec. 4, 1972which issued July 30, 1974 as U.S. Pat. No. 3,826,781.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to ethylene polymer based compositions which areuseful as primary insulation for copper conductors which are used inwire and cable which contain waterproofing filler and which can be usedunder elevated temperature conditions.

2. Description of the Prior Art

The current trend in the installation of telephone wire and cable whichcontains copper conductors is to install the wire or cable underground,in a duct, or by direct burial. To protect the wire or cable from waterdamage under such conditions, it is filled with waterproofing fillers.Filled cables of this type are disclosed in U.S. Pat. No. 3,668,298. Theuse of the waterproofing fillers in such cables, however, presentscompatability problems with respect to the polyolefin resin basedcompositions which have been used to date as the primary insulation forsuch wire and cable, and which primary insulation comes into contactwith the filler during the use of the wire and cable. If the polyolefinresin and the filler are too compatible the resin will absorb the fillerand swell and possibly also leach out from the insulation, stabilizersand other components of the insulation composition.

The selection of suitable synthetic resins for use as primary insulationin the filled wire or cable is further complicated by the fact that theresin based composition which must be used in this regard must be stablewith the filler at elevated temperatures of the order of about 40° to70° C. for extended periods of time, and the resin must also be stableduring extrusion thereof around the individual copper conductors atelevated temperatures of the order of about 200° to 300° C.

Although the filled wire or cable is installed underground wheretemperatures rarely reach a level which is likely to significantlyhasten the degradation of the insulation, there are portions of the wireor cable which will experience a more hostile environment. This occurswhen splices or tie-ins are made aboveground and the filler is removedfrom around a section of the conductor, and the insulated conductors arethen left exposed to the air. The exposed conductors are usually left inan enclosed box or pedestal in which temperatures approaching 70° C maybe reached in the field. The aging of the insulation in this environmentrepresents the most crucial test of insulation stability.

The extrusion of the primary insulation, and the use of the extrudedinsulation, under significantly different environmental conditions thanthose previously encountered also requires the use of antioxidants whichwill be effective under such conditions for the protection of theinsulation against oxidative degradation. The antioxidants to be used,however, must also be chemically and physically compatible with thefiller, and the other components of the insulation composition, and thecopper conductor itself.

Thus, the other components of the insulation compositions must alsoinclude copper deactivators to counteract the tendency of the copperconductor to catalytically influence the oxidative degradation of thesynthetic resin in the primary insulation and any absorbed filler.

Thus, the formulation of a primary insulation composition which will beuseful in contact with copper conductors and waterproofing fillers underelevated use temperatures, and after being subjected to elevatedextrusion temperatures, requires the use of a unique combination ofmaterials, which combinations are not readily achieved.

TEST PROCEDURES

To closely simulate actual extrusion and use conditions and thusfacilitate the development of useful primary insulation compositions,several test procedures were devised for the purposes of evaluatingcandidate insulation compositions.

PREPARATION OF CANDIDATE INSULATION COMPOSITIONS

The candidate insulation compositions were prepared by milling together,on a two-roll mill or in a Brabender mixer or in a Banbury mixer at atemperature of about 150° to 180° C., the components of each candidatecomposition, which usually comprised, in % by weight,

98.8% of candidate synthetic resin

1% of TiO₂ (to simulate pigment effect)

0.1% of candidate antioxidant

0.1% of candidate copper deactivator

The resulting compositions were then tested as 0.010 inch thick films,and/or after being extruded onto copper wire.

TESTING OF CANDIDATE INSULATION COMPOSITIONS AS FILM

When the candidate composition was tested as a film it was firstimmersed in a waterproofing filler for seven days at 70° C. with oneside of the film held in contact with a copper foil during this agingperiod. This test procedure is used because it simulates theenvironmental history of a portion of the insulation in a wire or cablewhich has experienced typical handling, including storage on reels insunlight, removal of filler for splicing operations and then permanentinstallation in splice boxes or pedestals above ground whereintemperatures may approach 70° C.

The waterproofing filler used in all of these test procedures was astabilized mixture of petroleum jelly and a homopolymer of ethylene.

The films were then wiped free of the waterproofing filler and were thenfurther tested by heat aging them in air at 120° C. in a circulating airoven while in contact, in the oven, with copper foil. The time tobrittleness was then recorded. Brittleness was determined by removingthe film from the oven once every 24 hours, allowing it to reach roomtemperature and flexing it. Brittleness was reached when the insulationfirst showed cracking. The films were returned to the oven, in contactwith the copper foil, between flexing tests.

The standard insulation composition against which the candidatecompositions were tested was a composition consisting of, in % byweight,

98.9% of the candidate synthetic resin

1.0% of TiO₂

0.1% of 4,4'-thiobis-(3-methyl-6-t-butyl phenol) (as antioxidant)

This standard insulation composition, when tested as a film or as wireinsulation as disclosed below, has an expected lifetime (L) at 43° C(simulated pedestal temperature) of L₄₃ = 100 years. This lifetime isarrived at from Arrhenius plots of temperature and lifetime at severaltemperatures. From these plots it is then possible to calculate apredicted lifetime (in years) at 43° C from a single measurement ofactual lifetime (in days) at 120° C in an oven aging test as describedbelow. This relationship is

    L.sub.43 (years) = 12.25 L.sub.120 (days)

The standard insulation composition's lifetime is L₁₂₀ = 8 days or L₄₃ =100 years.

TESTING OF CANDIDATE INSULATION COMPOSITION ON WIRE

When the candidate composition was tested after being extruded ontocopper wire, the composition was extruded onto a 19, 22 or 24 AWG singlecopper wire at an extrusion speed of about 2000 feet per minute whilethe composition was heated to a temperature of about 260° to 290° C. Thecandidate compositions were extruded onto the wire so as to provideinsulation coatings which were about 8 to 11 mils thick, depending onwire size.

A length of the insulated wire was then immersed in the waterproofingfiller for seven days at 70° C.

The test wire was then removed from the filler, wiped free of the fillerand then further tested by heat aging it in air at 70° - 160° C. in acirculating hot air oven. At temperatures of 70° - 120° C i.e., belowthe melting point of the polymer, the wire was aged in the form of"pigtail" specimens in which the wire was wrapped in a tight coil aboutits own diameter. At temperatures of >120° C straight lengths of wirewere aged. The time to brittleness of the insulation was then recorded.Brittleness was determined by removing the wire from the oven at variousintervals depending on the test temperature, and allowing it to reachroom temperature and by examining it for spontaneous cracking in thepigtail specimens or upon flexing the other samples. Brittleness wasreached when the insulation first showed cracking. The wires werereturned to the oven, between observations.

SUMMARY OF THE INVENTION

An object of the present invention is to provide primary insulationcompositions for copper conductors which are to be used in electricalwire and cable which is to be filled with waterproofing filler.

Another object of the present invention is to provide such insulationcompositions as will be useful for prolonged periods of time at elevatedtemperatures.

A further object of the present invention is to provide such insulationcompositions as can be useful after being extruded onto the copperconductors under high temperature extrusion conditions.

It has now been discovered that, and in accordance with the presentinvention, these and other objects are achieved by using as theinsulation composition one which comprises a selective combination ofcertain ethylene polymer as a base resin, certain nitrogen-containingcompounds as copper deactivating agents and certain high molecularweight organic compounds as antioxidants.

DESCRIPTION OF THE PREFERRED EMBODIMENT

It has now been found that the objects of the present invention can berealized by using as a primary insulation composition for copperconductors which are to be used in electrical wire and cable which is tobe filled with waterproofing filler and subjected to use temperatures ofabout 40° to 70° C. one which comprises

ethylene polymer having a density of about 0.928 to 0.955,

copper deactivating amounts of at least one organic compound which is anoxalyl dihydrazide, and

antioxidant effective quantities of at least one organic compound havinga molecular weight of ≧550, and which contains two or three hinderedphenolic hydroxyl groups, per molecule thereof.

ETHYLENE POLYMER

The ethylene polymer which is to be used as the base resin in theinsulation compositions of the present invention is a solid (at 25° C.)thermoplastic resin having a density of about 0.928 to 0.955 gr/cc(ASTM-1505 test procedure with conditioning as in ASTMD-1248-72). Thecomposition will contain about 95 to 99.8% by weight of such ethylenepolymer, based on the total weight of the composition.

The ethylene polymer component of the insulation composition of thepresent invention is comprised of one or more thermoplastic homopolymersor copolymers of ethylene which may be

a homopolymer of ethylene having a density of about 0.918 - 0.940,and/or

a copolymer of ethylene having a density of about 0.928 - 0.955.

The ethylene copolymers to be used in the compositions of the presentinvention are those of ethylene and one or more other linear C₃ to C₆alpha olefins. The other alpha mono-olefins would thus be propylene,butene-1, pentene-1, and hexene-1.

The copolymers will contain at least about 90% by weight of polymerizedethylene. The desired density range of the copolymers will dictate theexact amount of the other comonomer(s) which is to be used.

The ethylene polymer must also be readily extrudable, i.e. it must havea melt index of about 0.1 to 2 decigrams/minute (ASTM D-1238 at 44 psitest pressure).

COPPER DEACTIVATOR

The insulation compositions of the present invention also contain copperdeactivating amounts of one or more of the copper deactivating compoundsdescribed below. These copper deactivating amounts are usually of theorder of about 0.05 to 0.2% by weight, based on the total weight of theinsulation composition.

The copper deactivating agents to be used in the insulation compositionsof the present invention are organic nitrogen containing compounds,which are one or more oxalyl dihydrazides. These dihydrazides aredisclosed in U.S. Pat. No. 3,440,210, and have the structure ##STR1##wherein A and B are selected from the group consisting of a. H₂, and

b. benzyl type radicals having the structure ##STR2## Wherein R_(a) is amonovalent radical selected from the group consisting of hydrogen, C₁ toC₂₀ inclusive, alkyl and C₁ to C₂₀, inclusive, alkoxy, and X is selectedfrom the group consisting of hydrogen and the halogens, and

wherein at most one of A and B is H₂.

These copper deactivators include N,N'dibenzal (oxalyl dihydrazide) andN - benzal (oxalyl dihydrazide).

ANTIOXIDANT

The insulation compositions of the present invention also containantioxidant effective quantities of one or more of the antioxidantcompounds described below. These antioxidant effective quantities areusually of the order of about 0.01 to 0.2% by weight, based on the totalweight of the insulation composition.

The antioxidant compounds to be used in the insulation composition ofthe present invention are organic compounds which are other than thecopper deactivators and have molecular weights of at least 550 and areone or more compounds comprising two or three hindered phenolic hydroxylgroups per molecule thereof.

The phenolic hydroxyl groups are preferably hindered, partially orcompletely, with tertiary butyl groups.

The antioxidants would include diphenols and triphenols such as

1,3,5, trimethyl-2-4,6-tris(3,5-di-t-butyl-4-hydroxylbenzyl) benzene,

1,3,5,tris(3,5-di-t-butyl-4-hydroxybenzyl)-5-triazine-2,4,6(1H,3H,5H)-triones.

The antioxidants would also include diphenols having the structure##STR3## wherein R' is a tertiary butyl radical.

These phenolic antioxidants may be further modified by techniques knownto those in the art.

The antioxidant and copper deactivator are also preferably used in aweight ratio, to each other, of about 1 to 2.

ADJUVANTS

The insulation compositions of the present invention may also contain,in effective quantities thereof, one or more adjuvant materials whichare commonly employed in primary insulation compositions intended foruse in contact with copper conductors and waterproofing filler. Suchadjuvants would include color pigments such as titanium dioxide andcarbon black.

The total amount of such adjuvants which are used usually amounts to nomore than about 0.5 to 2% by weight, based on the total weight of theinsulation composition.

The insulation compositions of the present invention may also be used incellular form. To prepare the cellular compositions blowing agenteffective quantities of conventional blowing agents which are chemicallycompatible with the antioxidant and the copper deactivating agents areadmixed with the insulation composition and the resulting composition isthen blown, by conventional blowing techniques, as the insulation isapplied to the copper wire substrate.

WATERPROOFING FILLER

The waterproofing filler with which the primary insulating compositionsof the present invention are used are hydrophophic, hydrocarbon,moisture-barrier materials. They are usually waxy or jelly likematerials which are soft solids at 25° C and have melting points ofabout 50° to 80° C. These waterproofing fillers include petrolatumswhich are petroleum distillate residues, low molecular weight polyolefinresins, and mixtures thereof.

The following examples are merely illustrative of the present inventionand are not intended as a limitation upon the scope thereof.

EXAMPLES 1 - 7

For these examples various combinations of the copper deactivators andantioxidants of the present invention were blended together as describedabove with one part by weight, based on the weight of the totalcomposition, of TiO₂ and about 98.8 parts by weight, based on the weightof the total composition of a solid copolymer of ethylene and butene-1having a density of 0.950.

The resulting primary insulation compositions were tested as film (agingtest procedure A) or as extruded on wire (aging test procedure B) asdescribed above, and in contact with a waterproofing filler. This fillerwas either a blend of 85% by weight of petroleum jelly and 15% by weightof a low density (0.927) polyethylene or a blend of 92% by weight ofpetroleum jelly and 8% by weight of low density polyethylene (0.927).The 85/15 blend had a melting point of about 80° C, and the 92/8 blendhad a melting point of about 70° C. The 85/15 blend was stabilized with0.2% by weight of 4,4'-thiobis-(3-methyl-6-t-butyl phenol) and the 92/8blend was stabilized with 0.5% by weight of tetrakis[methylene-3,3',5-di-t-butyl-4'-hydroxyphenylpropionate] methane.

The following Table lists the specific copper deactivators andantioxidants, as well as the amounts thereof in % by weight, based onthe total weight of the composition, which were used in eachcomposition. The Table also lists the blend of filler (85/15 or 92/8)which was used with each composition, as well as the test procedure (Aor B) used with each composition. Finally the Table lists the L₁₂₀lifetime, in days, of each of these compositions. These L₁₂₀ lifetimesshow that the stabilized compositions of the present invention provideextremely good insulation for prolonged use under elevated temperatureconditions.

                                      TABLE                                       __________________________________________________________________________              Amt.                                                                          of Cu.                                                                            Anti-                                                                              Amt.of                                                          Cu   Deact.                                                                            Oxi- Antiox.                                                                            Filler                                                                             L.sub.120,                                                                         Aging                                       Example                                                                            Deact. *                                                                           %   dant **                                                                            %    Blend                                                                              days Test                                        __________________________________________________________________________    1.   --   0   AO-1 0.1  85/15                                                                               8   A                                           2.   CD-1  0.05                                                                             AO-1  0.05                                                                              85/15                                                                               7   A                                           3.   CD-1 0.1 AO-1 0.1  85/15                                                                              15   A                                           4.   CD-1 0.1 AO-2 0.1  92/8 16   A                                           5.   CD-1 0.1 AO-2 0.1  92/8 10   B                                           6.   CD-1 0.1 AO-3 0.1  92/8 18   A                                           7.   CD-1 0.1 AO-4 0.1  92/8 15-19                                                                              B                                           __________________________________________________________________________     * as used in the Table                                                        CD-1 is N,N'-dibenzal (oxalyl dihydrazide)                                    ** as used in the Table                                                       AO-1 is 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl)           benzene                                                                       AO-2 is 1,3,5-tris                                                            (3,5-di-t-butyl-4-hydroxybenzyl)benzene)-5-triazine-2,4,6(1H,3H,5H) trion     AO-3 is a modified AO-2 which has a molecular weight of >550 and contains     three hindered phenolic groups and is sold as Good-Rite (T.M.) 3125 by th     B. F. Goodrich Chemical Co., Cleveland, Ohio, U.S.A.                          ##STR4##     wherein R' is a tertiary butyl group.

What is claimed is:
 1. Insulated wire or cable having primary insulationbetween copper conductor and moisture barrier filler and wherein saidprimary insulation comprisessolid ethylene polymer having a density ofabout 0.928 to 0.955, copper deactivating amounts ofN,N'-dibenzal-(oxalyl dihydrazide), and antioxidant effective quantitiesof 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene.